1. Field of the Invention
The present invention relates to a packet transfer network in which packet transfer between a through a plurality of packet transfer devices provided therebetween and, more particularly, to a method of transmitting a label request packet for use in determining a label to be used among a plurality of packet transfer devices for packet transfer from a transmission side packet transfer device connected to a first terminal to a reception side packet transfer device connected to a second terminal.
2. Description of the Related Art
With reference to FIG. 16, a conventional packet transfer network will be described. The packet transfer network shown in FIG. 16 is a network in which first a label is determined according to a procedure called LDP (Label Distribution Protocol) among packet transfer devices to transfer a packet for inter-terminal communication with a determined label attached to the head thereof, thereby achieving high-speed packet transfer as recited in IETF Internet Draft “Multiprotocol Label Switching Architecture”.
FIG. 3 shows one example of such a packet with a label. More specifically, a labeled packet is composed of a communication packet and a label for transfer within a network. One kind of labeled packet is an ATM (Asynchronous Transfer Mode) cell. As is well known, an ATM cell has 53 bytes, of which 5 bytes form a header (cell header) and 48 bytes form an information field. A cell header includes a VCI (Virtual Channel Identifier) for identifying a connection to which an ATM cell belongs and a VPI (Virtual Path Identifier). The VCI and the VPI are among kinds of labels. A packet transfer device may divide a packet received from a terminal into a plurality of ATM cells and transmit the same.
The packet transfer network of this example is a packet transfer network having a first terminal 1011 and a second terminal 1012, between which first to fifth packet transfer devices 1001, 1002, 1003, 1004 and 1005 are provided. A packet transfer device selected as a route (path) is also called a repeating installation. In the illustrated example, the first terminal 1011 operates as a transmission terminal and the second terminal 1012 operates as a destination terminal.
In the following, description will be made of a procedure of determining a label for use among the first to fifth repeating installations (packet transfer devices) 1001 to 1005 for the packet transfer between the first terminal 1011 and the second terminal 1012 in particular with respect to an example recited in IETF Internet Draft “Constraint-Based LSP Setup Using LDP”.
In the figure, a packet transfer device (repeating installation) is indicated simply as a device. It should be noted here that a label is determined (allocated) for a link (path) between packet transfer devices (repeating installations) adjacent to each other. In addition, there are cases where the same label is allocated both for an up-direction and a down-direction and where different labels are allocated to them.
FIG. 17 to 19 show packets to be transferred between the first and the second terminals 1011 and 1012 for determining a label. FIG. 17 shows a label request packet, FIG. 18 shows a label allocation packet and FIG. 19 shows a state notification packet. The label allocation packet and the state notification packet are generally referred to as response packets. FIG. 20 shows a flow of operation of the packet transfer network illustrated in FIG. 16.
Assume that the first repeating installation 1001 receives a first packet from the first terminal 1011 as a transmission terminal to the second terminal 1012 as a destination terminal or a request is made by a network manager for the connection between the first terminal 1011 and the second terminal 1012. In this case, the first repeating installation 1001 is allowed to select one of a plurality of paths reachable from the first terminal 1011 to the second terminal 1012 to transmit a label request packet along the selected path. It is assumed here that a selected path passes through the second repeating installation 1002 and the fourth repeating installation 1004. In this case, the first repeating installation 1001 examines a label use condition of a link (transmission path) on the side of the second repeating installation 1002 and when there is a label value yet to be used, transmits the label request packet shown in FIG. 17 to the second repeating installation 1002 (an arrow A1 in FIG. 20).
As shown in FIG. 17, the label request packet transmitted by the first repeating installation 1001 is composed of an LDP label and an LDP packet. The LDP packet includes a label request packet identifier, a transmission terminal identifier, a destination terminal identifier and a plurality of repeating installation identifiers. In the case of the present example, the transmission terminal identifier indicates the first terminal 1011, the destination terminal identifier indicates the second terminal 1012 and the repeating installation identifiers indicate the second and the fourth repeating installations 1002 and 1004.
The second repeating installation 1002 receives the label request packet from the first repeating installation 1001. The second repeating installation 1002, since an element at the head of the repeating installation identifiers of the received label request packet (FIG. 17) is its own device identifier (device 1002), removes the element and refers to the next repeating installation identifier (device 1004) to select the third repeating installation 1003 as a subsequent transfer destination. In addition, the second repeating installation 1002 examines a label use condition of each transmission path on the side of the first repeating installation 1001 and the side of the third repeating installation 1003. At this time, when a label value yet to be used exists, the second repeating installation 1002 removes an information element of its own device identifier from the received label request packet and transmits the obtained packet to the third repeating installation 1003 (an arrow A2 in FIG. 20).
Upon receiving the label request packet from the second repeating installation 1002, the third repeating installation 1003 refers to an element at the head of the repeating installation identifiers of the received label request packet to select the fourth repeating installation 1004 as a subsequent transfer destination. In addition, the third repeating installation 1003 examines a label use condition of each transmission path on the side of the second repeating installation 1002 and on the side of the fourth repeating installation 1004. When there exists a label value yet to be used, the third repeating installation 1003 transmits the received label request packet to the fourth repeating installation 1004 without modification (an arrow A3 in FIG. 20).
The fourth repeating installation 1004 receives the label request packet from the third repeating installation 1003. The fourth repeating installation 1004, since the element at the head of the repeating installation identifiers of the received label request packet is its own device identifier (device 1004), removes the element. With no other information element, the fourth repeating installation 1004 refers to the destination terminal identifier in place of the elements to select the fifth repeating installation 1005 as a subsequent transfer destination. In addition, the fourth repeating installation 1004 examines a label use condition of each transmission path on the side of the third repeating installation 1003 and on the side of the fifth repeating installation 1005. When there is a label value yet to be used, the fourth repeating installation 1004 removes an information element of its own device identifier from the received label request packet and transmits the obtained packet to the fifth repeating installation 1005 (Step A4 in FIG. 20).
The fifth repeating installation 1005 receives the label request packet from the fourth repeating installation 1004. The fifth repeating installation 1005, since the destination terminal identifier indicates the second terminal 1012 which is connected directly to its own device, examines a label use condition of the transmission path on the side of the fourth repeating installation 1004. When there is a label value yet to be used, the fifth repeating installation 1005 inserts the value as an allocated label value into the label allocation packet shown in FIG. 18 and transmits the obtained packet to the fourth repeating installation 1004 (an arrow A5 in FIG. 20).
As shown in FIG. 18, the label allocation packet to be transmitted by the fifth repeating installation 105 is a packet indicative of an affirmative acknowledgment which is composed of an LDP label and an LDP packet. The LDP packet includes a label allocation packet identifier, a transmission terminal identifier, a destination terminal identifier and an allocated label. In the present example, the transmission terminal identifier indicates the first terminal 1011 and the destination terminal identifier indicates the second terminal 1012.
The fourth repeating installation 1004, upon receiving the label allocation packet from the fifth repeating installation 1005, takes out the allocated label value in a region of an allocated label. Subsequently, the fourth repeating installation 1004 stores a combination of the taken out allocated label value and the label value yet to be used on the side of the third repeating installation 1003, inserts a label value selected for the transmission path on the side of the third repeating installation 1003 into the label allocation packet and outputs the obtained packet to the third repeating installation 1003 (an arrow A6 in FIG. 20).
By the same procedure as that of the fourth repeating installation 1004, the third repeating installation 1003 and the second repeating installation 1002 output label allocation packets to the second repeating installation 1002 and the first repeating installation 1001 (arrows A7 and A8 in FIG. 20).
Upon receiving the label allocation packet from the second repeating installation 1002, the first repeating installation 1001 determines that label determination is made at all the repeating installations within the network and stores an allocated label value in the received label allocation packet. Then, the first repeating installation 1001 hereinafter attaches the label value in question to a packet bound for the second terminal 1002 which is received from the first terminal 1011 and outputs the obtained packet as a labeled packet to the second repeating installation 1002. The second, the third, and the fourth repeating installations 1002, 1003 and 1004 also replace labels of received packets based on stored label values. A labeled packet arriving at the fifth repeating installation 1005 is output to the second terminal 1012.
It is also assumed that each repeating installation receiving a label request packet examines a label use condition to find that it uses up all the labels. In this case, by transmitting such a state notification packet as shown in FIG. 19 to a repeating installation which has transmitted the label request packet, each repeating installation gives notification to the requesting source.
As illustrated in FIG. 19, the state notification packet is a packet indicative of a negative acknowledgment which is composed of an LDP label and an LDP packet. The LDP packet includes a state notification packet identifier and a state. Here, the state indicates “no label yet to be used”.
A repeating installation receiving a state notification packet one after another transmits a state notification packet of the same contents to a repeating installation having transmitted a label request packet, resulting in the state notification packet reaching the first repeating installation 1001 (arrows A9 to A11 in FIG. 20).
Upon receiving the state notification packet, the first repeating installation 1001 learns that its own label request is refused anywhere in the packet transfer network to start such processing as making a label request on another path again.
Concerning the present invention, various related techniques are known. Japanese Patent Laying-Open (Kokai) No. Heisei 1-120928 (hereinafter referred to as “related art 1”), for example, discloses “Instantaneous Packet Transfer Control System” which, when a packet required to have instantaneousness is transmitted in a packet switching network, as much as possible prevents transfer of invalid packets caused by an increase in a delay time to reduce invalid load on the packet switching network as much as possible. According to the instantaneous packet transfer control system disclosed in the related art 1, in a packet switching network made up of a plurality of packet switching systems, a packet to be transmitted within the packet switching network and required to have instantaneousness is provided with a region to which delay information indicative of a delay time caused while a packet is transferred in the packet switching network is attached. At each packet switching system, a delay time indicated by delay information contained in a packet arriving through an incoming trunk line and a delay time to be added before the packet is transmitted to an outgoing trunk line are added and a result of the addition is compared with a predetermined delay threshold. The system is designed such that when the addition result is less than the delay threshold value, the delay information contained in the packet is updated and transmitted to the outgoing trunk line. Then, when the addition result is not less than the delay threshold value, the packet is abandoned.
On the other hand, Japanese Patent Laying-Open (Kokai) No. Heisei 11-317749 (hereinafter referred to as related art 2) discloses “High-Speed Connection Setting/Releasing Method and Device Therefor” which realizes improvement in a calling processing capacity of a switching system and reduction in connection delay and enables application to a large-scale network and networks connected to each other without requiring hardware for transmission and reception of a special signal for connection setting. In the related art 2, each ATM exchange has a VCC management unit for managing VCC set in advance between exchanges, a band management unit for managing a band of VP, an accommodation terminal management unit for managing correspondence between a subscriber's terminal and an accommodation ATM exchange, and a switch unit for conducting connection and disconnection of a connection. In setting and releasing a connection, a signal for use in ordinary SVC services is transferred link by link. Then, at transmission side and reception side ATM exchanges, connection is set or released by connecting or disconnecting a VC captured on the side of a subscriber/on the side of other network and a repeating connection set in advance between the reception and transmission side exchanges.
Furthermore, Japanese Patent No. 2861771 (hereinafter referred to as related art 3) discloses “Signaling System Using Logical Repeating Path Information” which enables application to a large-scale network and setting and disconnection of a connection at a high-speed in a terminal connection/disconnection control procedure (signaling) system at a connection-oriented packet network. More specifically, according to the first mode of the related art 3, a transmission terminal has information about a logical repeating path from its own terminal to a reception terminal which is expressed as a pair of a physical port number and a logical multiple channel number, and a table of correspondence to an address of the reception terminal. Then, using logical repeating path information corresponding to the reception terminal which is indicated in the table, signaling is conducted. In addition, immediately after signaling is conducted by the transmission terminal using the logical repeating path information, the transmission terminal conducts data transfer before the reception terminal returns an acknowledgment of a logical channel connection. According to the second mode of the related art 3, a switch has information about a logical repeating path from its own switch to a reception terminal which is expressed as a pair of a physical port number and a logical multiple channel number, and a table of correspondence to an address of the reception terminal. Then, at the time of sending a signaling packet from a transmission terminal to the switch by using a reception terminal address, the switch, using the above-described table, converts a signaling packet using the reception terminal address into a signaling packet using the information about a logical repeating path from the switch to the reception terminal to conduct signaling. In addition, when the transmission terminal conducts signaling using a destination address, the transmission terminal conducts data transfer immediately after a switch accommodated in the transmission terminal returns an address conversion completion signal and before the reception terminal returns an acknowledgment of a logical channel connection. Moreover, when the transmission terminal conducts signaling using a destination address, the transmission terminal conducts data transfer immediately after a switch accommodated in the transmission terminal returns an address conversion completion signal and before the reception terminal returns an acknowledgment of a logical channel connection. In addition, a reference number is attached to logical repeating path information held by a switch, whereby the transmission terminal conducts signaling using the reference number. Moreover, in the above-described first and second modes, a logical output path is represented by a reference number and based on logical repeating path information obtained by linking the reference numbers, the transmission terminal conducts signaling.
The above-described conventional packet transfer networks, however, have the following problems.
The first problem is that because a label request packet is sequentially processed on and propagated through packet transfer devices (repeating installations) on a path, a waiting time of a packet transfer device (repeating installation) near a destination terminal for receiving a label request packet is increased.
The second problem is that because of the same cause as that of the first problem, time is increased for waiting for a label allocation packet or a state notification packet which are results (response packet) corresponding to a label request packet to return to a packet transfer device (repeating installation) as a transmission source of the label request packet.
The above-described related art 1 discloses only a technical idea of attaching delay information to a packet and discloses none of label request packet transmission methods. The related art 2 discloses only a technical idea of reducing the volume of processing related to header conversion table setting to improve a calling processing capacity of an exchange and reduce connection delay without requiring hardware for transmitting and receiving a special signal for connection setting and as well as the above-described related art 1 and 2, discloses none of label request packet transmission methods. Furthermore, the related art 3 disclosed only a signaling system using logical repeating related art 1 and 2, disclosed none of label request packet transmission methods.